The present invention relates to a polishing device for polishing or grinding a base plate surface to be used for a magnetic disc and the like.
An example of a conventional polishing device is explained hereunder with reference to FIG. 4.
First, a disc shape base plate (hereinafter referred to as a disc) made of aluminum, aluminum alloy or the like is prepared, and after the disc is subjected to a surface treatment or beveling working, a Ni-P plating layer is formed on the surface thereof.
Next, a surface of the Ni-P plating layer is polished or ground by a polishing device 30 as shown in FIG. 4 so that average coarseness Ra is 0.004 .mu.m and less.
A lower supporting portion 31 of the polishing device 30 includes an internal gear 32, a disc shape lower supporting member 33 and a sun gear 34 provided at a central portion of the lower supporting member 33. The lower supporting member 33 has a soft polishing pad 35, and is housed inside the internal gear 32. The gears 32 and 34 are rotated independently.
Also, carriers 36 are disposed on the lower supporting member 33, and have gear teeth, not shown, provided around the peripheries thereof for meshing with the internal gear 32 and the sun gear 34, and a plurality of through-holes 36a for holding the discs.
Further, although not shown, the polishing device 30 is provided with an upper supporting member having a polishing pad made of a soft material, such as foamed urethane, and a supply portion for supplying polishing particles.
In the polishing device 30 having the structure as described above, the upper supporting member is pressed against the lower supporting member 33 with a predetermined pressure, and while the polishing particles are supplying between the upper and lower supporting members through the supply portion, the internal gear 32, the lower supporting member 33, the sun gear 34 and the upper supporting member are rotated to thereby polish the discs.
When the discs are polished by the polishing device 30, the discs are held by the carriers 36 and rotated. However, since the carriers 36 are rotated freely, irregular rotations are given to the discs.
Thus, a regular working mark can not be obtained on the surfaces of the polished discs. When the regular working mark is not obtained, a subsequent texturing processing is also influenced, which finally results in a problem, such as a head crash or damages of the disc and head.
The present invention has been made in view of the foregoing problems of the conventional device.
Accordingly, one object of the invention is to provide a polishing device, wherein polishing efficiency can be extremely improved.
Another object of the invention is to provide a polishing device as stated above, wherein a regular working mark can be formed on a surface of a disc.
Further objects and advantages of the invention will be apparent from the following description of the invention.